If a note was previously working properly and now refuses to sound, there must be something on the reed, which is what the reed has captured. This is usually due to excessive moisture in the mouth. Put the mouthpiece of the harmonica on the palm of your hand and take a few shots, then blow it in and out quickly on the blocked blowhole; this will usually clear the excess water and solve the problem of being blocked.

If the problem persists, then the note is still blocked, so the reed is usually something that captures something solid, such as a small piece of hair. Take a wooden toothpick and place it in an unvoiced hole, and gently push the corresponding reed. Note that the blowing reeds should be those that can be seen against the blowhole.

If it still does not solve the problem, then screw the screws on both ends of the harmonica and remove the cover. Remember to put the screw in the cover to avoid losing it. Check the reeds that aren't sounding, and you should find out what the reeds "caught" in the end. Use a wooden toothpick to gently push the reed out (it will be easier to do this after removing the cover), the card will fall off, and the problem will be solved.